Abstract

New Hawaii-MR1 sonar data show that the southernmost Mid-Atlantic Ridge joins the South American–Antarctic Ridge by an obliquely opening rift and overlaps Spiess Ridge, the westernmost segment of the Southwest Indian Ridge, with no evidence for a transform fault. The junction is therefore neither ridge-fault-fault nor ridge-ridge-ridge. We speculate that growth of Spiess Ridge adjacent to the triple junction has caused this complexity and discuss more generally the origins of distributed deformation at oceanic triple junctions.